Petroleum streams that contain metals are typically problematic in refineries as streams because the metallic components contained therein have a negative impact on certain refinery operations. Thus, demetallation has been referred to as critical to help conversion of crude fractions (see, e.g., Branthaver, Western Research Institute in Ch. 12, "Influence of Metal Complexes in Fossil Fuels on Industrial Operations", Am. Chem. Soc. Symp. Series No. 344 (1987)).
The presence of such metals prevents more advantageous use of the petroleum stream by rendering especially the heaviest oil fractions (in which these metal containing structures concentrate) less profitable to upgrade, and when these resources are used they make catalyst replacement/disposal expensive. Current refinery technologies typically address the problem by using metal containing feedstreams as a less preferred option, and by tolerating catalyst deactivation when there are not other feedstream alternatives available.
Treatment of petroleum resids to remove metals in the presence of air and a 50% NaOH solution with strong oxidants (sodium hypochlorite and peroxyacetic acid) are disclosed in Gould (Fuel, Vol. 59, p. 733, October 1980). Gould disclosed negligible metals removal with NaOH and air and no metals removed with air alone at 100.degree. C. Additionally, essentially no demetallation was achieved in Gould when a weak oxidizing agent was used. It was concluded that stronger oxidants than air were required.
U.S. Pat. No. 3,971,713 discloses a process for desulfurizing crude oils using solid calcium hydroxide at atmospheric pressure. Vanadium removal is also disclosed. However, the process is carried out at temperatures below about 100.degree. F. because desulfurization decreases at higher temperatures. The addition of water had a detrimental effect on the process as well. This would suggest that the use of aqueous calcium hydroxide is precluded. This process would be of limited application for treatment of resids, which are characterized by much higher viscosities than whole crude.
By contrast there exist a body of art related to the removal of non-metals, e.g., sulfur, which use phase transfer agents but typically require the presence of a strong oxidizing agent such as H.sub.2 O.sub.2 (see, e.g., Collins, et al., J. Molecular Catalysis A: Chemical 117, 397-403 (1997)). Use of the oxidant often also must be combined with additional processing steps (e.g., adsorption) in order to remove the oxygenated sulfur compounds from the treated stream. Treatment of petroleum feeds with base has been practiced to remove certain acids see, e.g., Kalichevsky and Kobe, eds., Petroleum Refinery With Chemicals, Elsevier Publ., 1956; Sartori, et al, International Application No. PCT/US96/13688 (Int'l. Publ. No. WO 97/08270) which discloses treatment with Group IA or IIA oxides, hydroxides or hydrates. U.S. Pat. No. 5,683,626 which discloses treatment of with tetraalkylammonium hydroxides to decrease crude acidity.
One skilled in the art would not expect that processes for removal of sulfur or naphthenic acids would be applicable to demetallation of petroleum streams because sulfur and naphthenic acids are not metals and would not be expected to behave as such.
It would be desirable to develop a process that would permit demetallation to be carried out at mild process conditions using air or oxygen rather than the stronger oxidizing agents (H.sub.2 O.sub.2 and stronger) that are typically used.